In general, ink-jet inks are either dye- or pigment-based inks. Both are typically prepared in an ink vehicle that contains the dye and/or the pigment. Dye-based ink-jet inks generally use a soluble colorant that is usually water-based to turn the media a specific color. Conversely, pigmented inks typically use an insoluble or dispersed colorant to achieve color.
Color characteristics of dye-containing inks play an important role in the quality of the printed ink-jet image. Perceived color quality can be characterized using any one of several color space systems, such as CIELAB, as is well known in the art. With respect to CIELAB color space, a color is defined using three terms L*, a*, and b*. With this system, L* defines the lightness of a color, and it ranges from 0 to 100 (with 100 being white). Additionally, the terms a* and b*, together, define the hue, where a* ranges from a negative number (green) to a positive number (red), and b* ranges from a negative number (blue) to a positive number (yellow). Additional terms such as h° (hue angle) and C* (chroma) are used to further describe a given color, as is known to those skilled in the art. A single ink-jet ink of a first color that has good chroma, gamut, hue angle, and light fastness is not always optimal for use with other colors. In other words, not only does an individual color, i.e., cyan, magenta, or yellow, have to have acceptable color qualities, but the ink-set in which it is used also plays a role in whether the ink-jet ink performs in an acceptable manner. Thus, the appropriate combining of certain dyes together for use in an ink-set can improve image quality.
Accordingly, investigations continue into developing dye sets that have improved properties and that do not improve one property at the significant expense of the others.